Photochromic materials are typically materials that have a function (light modulation function) that enables them to reversibly change color (visible light transmittance) as a result of undergoing an isomerization reaction when irradiated with light, and not only materials prior to being irradiated with light, but also materials formed after being irradiated with light, are referred to as photochromic materials. Consequently, photochromic materials are used as eyeglasses for preventing glare, optical switches as well as display materials such as ink having the ability to switch between display and non-display status. In addition, research is also proceeding on their application to optical discs and other recording materials as well as holograms.
Changes in color demonstrated by photochromic materials are typically expressed as a reversible chemical reaction of a material that is induced when the material is irradiated with light. Typical known examples of photochromic materials include spiropyran-based compounds, spirooxadine-based compounds, naphthopyran-based compounds, fulgide-based compounds, and diarylethene-based compounds (see, for example, Non-Patent Document 1). In addition, compounds having a novel structure that demonstrate rapid photoreactivity have also been recently reported (see, for example, Non-Patent Document 2).
Photochromic materials are broadly divided into those that exhibit a phenomenon referred to as positive photochromism, which causes these materials to change from an uncolored form to a colored form (colored state) accompanying a structural change when irradiated with light, and those that exhibit a phenomenon referred to as negative photochromism (reverse photochromic materials), which causes these materials to conversely change from a colored form (colored state) to an uncolored form when irradiated with light.
Several examples of these reverse photochromic materials have been reported, including spirobenzopyran derivatives (Patent Document 1), dimethyldihydropyrene derivatives (Patent Document 2), and diarylethene derivatives (Patent Document 3).